RAF hybrid build

[idahodreamer]

I thought I'd finally post some pics of my rebuild project. I'm using a stock raf as the "parts" aircraft to build a hybrid and comply with the 51% rule.

This is the original RAF before I tore it to pieces, if anyone recognizes it and knows it's history let me know I don't know much.


So far I have fabricated an all new rolling airframe with a 6" drop and suspension system. I plan to use the stock tail mounted 8" back from the stock position




I have the engine mounts temporarily installed to get everything adjusted square.

 

[Rehan K.Janjua]

Keep it up, looks good.

Drop keel, lower thrust, H/stub etc are the essence of a wonderful
Dreamer RAF.
For positive rotor AOA, look into a stabulator installation too.

Bet it would be fun to fly.

Good Luck.
Rehan

 

[Mike484]

This should be very interesting, please keep us posted.

 

[PW_Plack]

Bruce, it looks as if you're moving the engine lower, which gives up a big potential contribution of its weight toward the goal of getting the thrust aligned with CG. The most efficient reconfiguration (most effect for smallest move) leaves the engine's mass high, but inverts the reduction drive so the prop moves below the crankshaft rather than above it.

Have you done the math to see where the new CG will be?

Good looking work! I hope we get to see you and this machine at ROTR in June!

 

[GyroDoug]

Bruce,

Great job so far! It looks like you're getting right after it. I can't wait to see your finished product. You ought to come to our chapter meeting this weekend and spend some time talking to Curt about some of the issues you are into, since he did a major conversion to his RAF, he wouls be a very good resource for you and now that you are in the middle of the conversion you will know some of the right questions to ask. I know it's a pretty long drive for you but it will be a little closer because it's at Curt's hangar in Brigham city rather than in Spanish Fork, and Curt will be there which he isn't always at our other meetings so the time is right if you feel up for a healthy drive this weekend. Best of luck with your project! and we'll see you when we see you.

Doug Barker
URA Pres.

 

[StanFoster]

Bruce- Looks good! To further add to what Paul just said, when you lower the engine, not only does your thrustline get lowered, but so does your CG. Let's say your engine and prop that you are lowering weigh 250 pounds and your gyro with you in it weigh 1000 pounds. This engine and prop are 1/4 the total weight. Whatever amount in inches you lower your engine and prop, the CG will lower 1/4 th the distance you lowered the engine and prop. So say you lowered your engine 6 inches, the CG will drop 1.5 inches, giving you a 4.5 inch less thrustline offset. That's good, but as Paul stated, if the engine remained high and the prop lowered, you would have a larger reduction in thrustline off set. Lowering the whole engine and prop wastes some of the distance that the thrustline is lowered. Stan

 

[LARRYEBOYER]

ANOTHER WAY TO LOOK AT IT WHEN I DID THE FIRST DROP KEEL ON A RAF IN THE US IS WHAT DON PARHAM TOLD ME. YOU DROPPED THE ENGINE, BUT MATHMATICALLY YOU RAISED THE CABIN. cABIN WEIGHT, GAS, 2 PILOTS , INSTRIMENTS, SEAT, ECT. The math worked out to be 4.5 inches high thrust line.The effort to make a keel change is worth it. Just ask anyone who did it. Next best is to add an efective stab. We dropped the keel on my brother-in-laws RAF and he just loves how it flies.Good luck.
Stan raises an interesting point, but cost also enters in. Making a new redrive is expensive. My drop keel conversion was a couple hundred bucks. Sparrowhawks approach was up to $10000. And a lot of extra weight over a stock RAF. I flew the Sparrow hawk and then flew the drop keel/drop engine RAF. The RAF was as good or better.

 

[Aussie_Paul]

ANOTHER WAY TO LOOK AT IT WHEN I DID THE FIRST DROP KEEL ON A RAF IN THE US IS WHAT DON PARHAM TOLD ME. YOU DROPPED THE ENGINE, BUT MATHMATICALLY YOU RAISED THE CABIN. cABIN WEIGHT, GAS, 2 PILOTS , INSTRIMENTS, SEAT, ECT. The math worked out to be 4.5 inches high thrust line.The effort to make a keel change is worth it. Just ask anyone who did it. Next best is to add an efective stab. We dropped the keel on my brother-in-laws RAF and he just loves how it flies.Good luck.
Stan raises an interesting point, but cost also enters in. Making a new redrive is expensive. My drop keel conversion was a couple hundred bucks. Sparrowhawks approach was up to $10000. And a lot of extra weight over a stock RAF. I flew the Sparrow hawk and then flew the drop keel/drop engine RAF. The RAF was as good or better.

Spot on with what I discovered during my RAF, Hybrid, Firebird testing years ago.

Aussie Paul.

 

[idahodreamer]

From previous posts I know I won't get 6 inches closer to CG. I haven't done any math on it and figure I'll do a double hang test when I'm done and see where I end up. I will be putting the best HS I can find on it but haven't really thought about adding a stabilator also. Does anyone have any cost or availability information? RAF sa wanted to charge me $600 for a replacement set of build manuals when I contacted them a while back so I figured a stabilator would be in the arm and a leg category.

 

[Mike484]

Send me a PM with youe email address and I'll send you the build manual in a PDF. It is for my 1999 RAF but should have just about everything you need.

 

[idahodreamer]

thanks for the offer Mike but other kind souls from the forum have already supplied me with a manual.

 

[animal]

It looks good, keep us posted, I always have liked a drop keel RAF over the sparrow hawk. dragonflyerthom has a real nice one he built.

 

[Riff Raf]

Looks good, and looks vary familiar…Hmmm
I like Larry’s stab, that’s what I have on mine and it flies quite well.

 

[MichaelBurton]

I have flown several RAF configurations and all of the GBA Sparrowhawks.

Here is what I found.

The seats in the RAF are painful to sit in. The cabin is too small for me or any pilot over 6'.

The Sparrowhawk 1-3 Require more HP to fly than the RAF or any RAF mod. They are very stable and much more comfortable than the RAF. The also hold more fuel. The doors on the SH1 did not fit as well as on the SH 2-3

The Sparrowhawk 2-3 have space for tall pilots. I have tested with pilots over 6' 3" the SH1 is good for pilots up to 6' 2" This was the best for taller/bigger pilots

The 4" drop keel with HS on an otherwise unmodified RAF still has significant pushover potential and needs to be flown to take this into account.

The 4" Drop keel with HS, inverted PSRU and raised engine Had little pushover and is a good performer. I would like this option if I were smaller and the seats were nicer.

The GBA mod of the RAF is stable and easy to fly and had no pushover.
This mod It is a bit slower than the original RAF or any of the other mods I have flown. I like the big rudder. It is also takes more pedal force to steer this on the ground. It has the original cabin and seats. This is also a nice option for smaller pilots. It is still a good performer.

The 4" drop combined with small shocks and the inverted PSRU and raised engine was by far my favorite RAF mod for smaller pilots. I could not get over how well this worked. If the seats were not made to cause pain this would be my choice of mods. Add differential breaks, a castor on the nose wheel and chocolate for the ultimate RAF mod.

 

[idahodreamer]

Thanks for your input Mike, you'll probably get a chance to fly this one also as I still plan to come to you for training when the build is done and the time is right.

I do have a couple questions for those out there.

The build videos and build manuals I have aren't necessarily for the same year Raf but I see that the video I have says that the engine mount should be 1 degree angled upwards but the manual says that the mounts should be plumb with the keel. which is right? I originally assumed I would want engine thrust square with mast and keel.

Also to anyone who has done this keel drop mod; where did you end up mounting the battery? On the keel with new longer cables looks the easiest but would like to keep the weight as high as possible. Another thing I ran into was when lowering the engine but not the upper motor mount bracket the radiator fill tube is now 6" lower than the motor mount that it was originally attached to. Anyone come up with a good solution for this? At this time I'm thinking a 6" piece of redi-rod as a spacer through the original mounting holes.